Depends on how my neck feels and type of ride.
An old C1-C2 neck injury flares up occasionally and I'll need to stop more often to stretch and massage the muscle cramps along the neck and shoulder. On good days I might stop every couple of hours. On bad days, either more often or I'll cut the ride short.
For planned longer rides on good days without significant neck pain, I carry enough water and food that I don't need to stop to refuel anywhere. Depending on weather I might stop every couple of hours for a few minutes, but not too long. My legs stiffen up and feel dead if I stop too long. But an occasional short break, or soft pedaling for a few minutes, can feel refreshing.
For interval sessions I don't stop completely but soft pedal as appropriate for the workout plans. Same with running sessions. Those are usually about an hour, including warm up and cool down, so neck pain usually isn't much of an issue.
On fast group rides, I go by the ride leader's preferences. Those are usually 4-6 hours, with one planned rest stop for 15-20 minutes. There are regroup points, usually after long climbs, but the last straggler rarely gets a real rest break -- as soon as the last straggler catches up the group goes again. If I can't hang with the group, I'll drop off and go my own way. Often I'll finish the same distance but a little slower. That happens more often now, as I'm 63 and most folks in the faster groups are well under age 50. If the group are mostly 20s-40s, I know I'll be dropped within an hour. But that's how it goes with those rides.
On casual group rides we stop and regroup or rest as needed for the slowest or least fit participant. That's the whole purpose of some rides, to encourage newbies to keep coming back, get fitter and faster. If other folks are too impatient for that, there are other rides they can join.